Optical transmission networks allow all-optical transmission between network nodes. Traffic is carried by optical channels, called lambdas, and optical switching technology, such as Wavelength Selective Switches (WSS), allow lambdas to be switched at nodes.
A control plane can be added to this kind of network to allow automated set-up of paths, tear-down of paths and traffic recovery when faults occur in the network. A possible control plane is the Generalized Multi Protocol Label Switching (GMPLS) protocol suite being developed by the Internet Engineering Task Force (IETF). The GMPLS application for optical networks is called Wavelength Switched Optical Network (WSON).
One issue in this type of network is the relatively long time required to set-up a path. This is a particular problem during traffic recovery operations. When a fault occurs in the network, it is desirable that traffic is transferred to an alternative path as quickly as possible. Delay in setting up the alternative path can result in heavy loss of traffic.